A. Wound Healing and Growth Factors
Wound healing, the repair of lesions, begins almost instantly after injury. It requires the successive coordinated function of a variety of cells and the close regulation of degradative and regenerative steps. The proliferation, differentiation and migration of cells are important biological processes which underlie wound healing, which also involves fibrin clot formation, resorption of the clot, tissue remodeling, such as fibrosis, endothelialization and epithelialization. Wound healing involves the formation of highly vascularized tissue that contains numerous capillaries, many active fibroblasts, and abundant collagen fibrils, but not the formation of specialized skin structures.
The process of wound healing can be initiated by thromboplastin which flows out of injured cells. Thromboplastin contacts plasma factor VII to form factor X activator, which then, with factor V and in a complex with phospholipids and calcium, converts prothrombin into thrombin. Thrombin catalyzes the release of fibrinopeptides A and B from fibrinogen to produce fibrin monomers, which aggregate to form fibrin filaments. Thrombin also activates the transglutaminase, factor XIIIa, which catalyzes the formation of isopeptide bonds to covalently cross-link the fibrin filaments. Alpha.sub.2 -antiplasmin is then bound by factor XIII onto the fibrin filaments to thereby protect the filaments from degradation by plasmin (see, for example, Doolittle et al., Ann. Rev. Biochem. 53:195-229 (1984)).
When a tissue is injured, polypeptide growth factors, which exhibit an array of biological activities, are released into the wound where they play a crucial role in healing (see, e.g., Hormonal Proteins and Peptides (Li, C.H., ed.) Volume 7, Academic Press, Inc., New York, N.Y. pp. 231-277 (1979) and Brunt et al., Biotechnology 6:25-30 (1988)). These activities include recruiting cells, such as leukocytes and fibroblasts, into the injured area, and inducing cell proliferation and differentiation. Growth factors that may participate in wound healing include, but are not limited to: platelet-derived growth factors (PDGFs); insulin-binding growth factor-1 (IGF-1); insulin-binding growth factor-2 (IGF-2); epidermal growth factor (EGF); transforming growth factor-.alpha. (TGF-.alpha.); transforming growth factor-.beta. (TGF-.beta.); platelet factor 4 (PF-4); and heparin binding growth factors one and two (HBGF-1 and HBGF-2, respectively).
PDGFs are stored in the alpha granules of circulating platelets and are released at wound sites during blood clotting (see, e.g., Lynch et al., J. Clin. Invest. 84:640-646 (1989)). PDGFs include: PDGF; platelet derived angiogenesis factor (PDAF); TGF-.beta.; and PF-4, which is a chemoattractant for neutrophils (Knighton et al., in Growth Factors and Other Aspects of Wound Healing: Biological and Clinical Implications, Alan R. Liss, Inc., New York, N.Y., pp. 319-329 (1988)). PDGF is a mitogen, chemoattractant and a stimulator of protein synthesis in cells of mesenchymal origin, including fibroblasts and smooth muscle cells. PDGF is also a nonmitogenic chemoattractant for endothelial cells (see, for example, Adelmann-Grill et al., Eur. J. Cell Biol. 51:322-326 (1990)).
IGF-1 acts in combination with PDGF to promote mitogenesis and protein synthesis in mesenchymal cells in culture. Application of either PDGF or IGF-1 alone to skin wounds does not enhance healing, but application of both factors together appears to promote connective tissue and epithelial tissue growth (Lynch et al., Proc. Natl. Acad. Sci. 76:1279-1283 (1987)).
TGF-.beta. is a chemoattractant for macrophages and monocytes. Depending upon the presence or absence of other growth factors, TGF-.beta. may stimulate or inhibit the growth of many cell types. For example, when applied in vivo, TGF-.beta. increases the tensile strength of healing dermal wounds. TGF-.beta. also inhibits endothelial cell mitosis, and stimulates collagen and glycosaminoglycan synthesis by fibroblasts.
Other growth factors, such as EGF, TGF-.alpha., the HBGFs and osteogenin are also important in wound healing. EGF, which is found in gastric secretions and saliva, and TGF-.alpha., which is made by both normal and transformed cells, are structurally related and may recognize the same receptors. These receptors mediate proliferation of epithelial cells. Both factors accelerate reepithelialization of skin wounds. Exogenous EGF promotes wound healing by stimulating the proliferation of keratinocytes and dermal fibroblasts (Nanney et al., J. Invest. Dermatol. 83:385-393 (1984) and Coffey et al., Nature 328:817-820 (1987)). Topical application of EGF accelerates the rate of healing of partial thickness wounds in humans (Schultz et al., Science 235:350-352 (1987)). Osteogenin, which has been purified from demineralized bone, appears to promote bone growth (see, e.g., Luyten et al., J. Biol. Chem. 264:13377 (1989)). In addition, platelet-derived wound healing formula, a platelet extract which is in the form of a salve or ointment for topical application, has been described (see, e.g., Knighton et al., Ann. Surg. 204:322-330 (1986)).
The Heparin Binding Growth Factors (HBGFs), also known as Fibroblast Growth Factors (FGFs), which include acidic HBGF (aHBGF also known as HBFG-1 or FGF-1) and basic HBGF (bHBGF also known as HBGF-2 or FGF-2), are potent mitogens for cells of mesodermal and neuroectodermal lineages, including endothelial cells (see, e.g., Burgess et al., Ann. Rev. Biochem. 58:575-606 (1989)). In addition, HBGF-1 is chemotactic for endothelial cells and astroglial cells. Both HBGF-1 and HBGF-2 bind to heparin, which protects them from proteolytic degradation. The array of biological activities exhibited by the HBGFs suggests that they play an important role in wound healing.
Basic fibroblast growth factor (FGF-2) is a potent stimulator of angiogenesis and the migration and proliferation of fibroblasts (see, for example, Gospodarowicz et al., Mol. Cell. Endocinol. 46:187-204 (1986) and Gospodarowicz et al., Endo. Rev. 8:95-114 (1985)). Acidic fibroblast growth factor (FGF-1) has been shown to be a potent angiogenic factor for endothelial cells (Burgess et al., supra, 1989). However, it has not been established if any FGF growth factor is chemotactic for fibroblasts.
Growth factors are, therefore, potentially useful for specifically promoting wound healing and tissue repair. However, their use to promote wound healing has yielded inconsistent results (see, e.g., Carter et al., in Growth Factors and Other Aspects of Wound Healing: Biological and Clinical Implications, Alan R. Liss, Inc., New York, N.Y., pp. 303-317 (1988)). For example, PDGF, IGF-1, EGF, TGF-.alpha., TGF-.beta. and FGF (also known as HBGF) applied separately to standardized skin wounds in swine had little effect on the regeneration of connective tissue or epithelium in the wounds (Lynch et al., J. Clin. Invest. 84:640-646 (1989)). Of the factors tested, TGF-.beta. stimulated the greatest response alone. However, a combination of factors, such as PDGF-bb homodimer and IGF-1 or TGF-.alpha. produced a dramatic increase in connective tissue regeneration and epithelialization. (Id.) Tsuboi et al. have reported that the daily application of bFGF to an open wound stimulated wound healing in healing-impaired mice but not in normal mice (J. Exp. Med. 172:245-251 (1990)). On the other hand, the application to human skin wounds of crude preparations of porcine or bovine platelet lysate, which presumably contained growth factors, increased the rate at which the wounds closed, the number of cells in the healing area, the growth of blood vessels, the total rate of collagen deposition and the strength of the scar tissue (Carter et al., supra).
The reasons for such inconsistent results are not known, but might be the result of difficulty in applying growth factors to a wound in a manner in which they can exhibit their normal array of biological activities. For example, it appears that some growth factor receptors must be occupied for at least 12 hours to produce a maximal biologic effect (Presta et al., Cell Regul. 2:719-726 (1991) and Rusnati et al., J. Cell Physiol. 154:152-161 (1993)). Because of such inconsistent results, the role played by exogenously applied growth factors in stimulating wound healing is not clear. Further, a means by which growth factors might be applied to wounds to produce prolonged contact between the wound and the growth factor(s) is not presently known.
B. TSs
Surgical adhesives and TSs which contain plasma proteins are used for sealing internal and external wounds, such as in bones and skin, to reduce blood loss and maintain hemostasis. Such TSs contain blood clotting factors and other blood proteins. FG, also called fibrin sealant, is a gel similar to a natural clot which is prepared from plasma. The precise components of each FG are a function of the particular plasma fraction which is used as a starting material. Fractionation of plasma components can be effected by standard protein purification methods, such as ethanol, polyethylene glycol, and ammonium sulfate precipitation, ion exchange, and gel filtration chromatography. Typically FG contains a mixture of proteins including traces of albumin, fibronectin and plasminogen. In Canada, Europe and possibly elsewhere, commercially available FG typically also contains aprotinin as a stabilizer.
FGs generally are prepared from: (1) a fibrinogen concentrate, which contains fibronectin, Factor XIII, and von Willebrand factor; (2) dried human or bovine thrombin; and (3) calcium ions. Commercially prepared FGs generally contain bovine components. The fibrinogen concentrate can be prepared from plasma by cryoprecipitation followed by fractionation, to yield a composition that forms a sealant or clot upon mixture with thrombin and an activator of thrombin such as calcium ions. The fibrinogen and thrombin concentrates are prepared in lyophilized form and are mixed with a solution of calcium chloride immediately prior to use. Upon mixing, the components are applied to a tissue where they coagulate on the tissue surface and form a clot that includes cross-linked fibrin. Factor XIII, which is present in the fibrinogen concentrate, catalyzes the cross-linking.
Australian Patent 75097/87 describes a one-component adhesive, which contains an aqueous solution of fibrinogen, factor XIII, a thrombin inhibitor, such as antithrombin III, prothrombin factors, calcium ions, and, if necessary, a plasmin inhibitor. Stroetmann, U.S. Pat. Nos. 4,427,650 and 4,427,651, describes the preparation of an enriched plasma derivative in the form of a powder or sprayable preparation for enhanced wound closure and healing that contains fibrinogen, thrombin and/or prothrombin, and a fibrinolysis inhibitor, and may also contain other ingredients, such as a platelet extract. Rose et al., U.S. Pat. Nos. 4,627,879 and 4,928,603, disclose methods for preparing cryoprecipitated suspensions that contain fibrinogen and Factor XIII and their use to prepare a FG. JP 1-99565 discloses a kit for the preparation of fibrin adhesives for wound healing. Alterbaum (U.S. Pat. No. 4,714,457) and Morse et al. (U.S. Pat. No. 5,030,215) disclose methods to produce autologous FG. In addition, improved FG delivery systems have been disclosed elsewhere (Miller et al., U.S. Pat. No. 4,932,942 and Morse et al., PCT Application WO 91/09641).
IMMUNO AG (Vienna, Austria) and BEHRINGWERKE AG (Germany) (Gibble et al., Transfusion 30:741-747 (1990)) presently have FGs on the market in Europe and elsewhere (see, e.g., U.S. Pat. Nos. 4,377,572 and 4,298,598, which are owned by IMMUNO AG). TSs are not commercially available in the U.S. However, the American National Red Cross and BAXTER/HYLAND (Los Angeles, Calif.) have recently co-developed a FG (ARC/BH FG) which is now in clinical studies.
The TSs which are used clinically outside of the U.S. pose certain clinical risks and have not been approved by the Food and Drug Administration for use in the U.S.A. For example, the TSs available in Europe contain proteins of non-human origin such as aprotinin and bovine thrombin. Since these proteins are of non-human origin, people may develop allergic reactions to them. In Europe heat inactivation is used to inactivate viruses which may be present in the components of the FG. However, this heat inactivation method may produce denatured proteins in the FG which may also be allergenic. In addition, there is concern that this inactivation method will not inactivate prions which cause bovine spongiform encephalopathy, "mad cow disease," which may be present in the TS due to the use of bovine proteins therein. Since this disease appears to have already crossed from sheep, in which it is called "scrapies," to cows, it is not an insignificant concern that it could infect humans.
The ARC/BH FG has advantages over the TSs available in Europe because it does not contain bovine proteins. For example, the ARC/BH TS contains human thrombin instead of bovine thrombin and does not contain aprotinin. Since the ARC/BH FG does not contain bovine proteins it should be less allergenic in humans than those TSs available in Europe. In addition, the ARC/BH FG is virally inactivated by a solvent detergent method which produces fewer denatured proteins and thus is less allergenic than those available in Europe. Therefore, the ARC/BH FG possesses advantages over the TSs which are now commercially available in other countries.
FG is primarily formulated for clinical topical application and is used to control bleeding, maintain hemostasis and promote wound healing. The clinical uses of FG have recently been reviewed (Gibble et al., Transfusion 30:741-747 (1990); Lerner et al., J. Surg. Res. 48:165-181 (1990)). By sealing tissues FG prevents air or fluid leaks, induces hemostasis, and may contribute to wound healing indirectly by reducing or preventing events which may interfere with wound healing such as bleeding, hematomas, infections, etc. Although FG maintains hemostasis and reduces blood loss, it has not yet been shown to possess true wound healing properties. Because FG is suitable for both internal and external injuries, such as bone and skin injuries, and is useful to maintain hemostasis, it is desirable to enhance its wound healing properties.
FG with a fibrinogen concentration of approximately 39 g/l and a thrombin concentration of 200-600 U/ml has produced clots with significantly increased stress, energy absorption and elasticity values (Byrne et al., Br. J. Surg. 78:841-843 (1991)). Perforated Teflon cylinders filled with fibrin clot (5 mg/ml) and implanted subcutaneously stimulated the formation of granulation tissue, including an increased precipitation of collagen, when compared to empty cylinders (Hedelin et al., Eur. Surg. Res. 15:312 (1983)).
C. Bone Wounds and Their Repair
The sequence of bone induction was first described by Urist et al. using demineralized cortical bone matrix (Clin. Orthop. Rel. Res. 71:271 (1970) and Proc. Natl. Acad. Sci. USA 70:3511 (1973)). Implanted subcutaneously in allogeneic recipients, demineralized cortical bone matrix releases factors which act as local mitogens to stimulate the proliferation of mesenchymal cells (Rath et al., Nature (Lond.) 278:855 (1979)). New bone formation occurs between 12 and 18 days postimplantation. Ossicle development replete with hematopoietic marrow lineage occurred by day 21 (Reddi, A., In Extracellular Matrix Biochemistry (Piez et al., ed.) Elsevier, New York, N.Y., pp. 375-412 (1984)).
Demineralized bone matrix (DBM) is a source of osteoinductive proteins known as bone morphogenetic proteins (BMP), and growth factors which modulate the proliferation of progenitor bone cells (see, e.g., Hauschka et al., J. Biol. Chem. 261:12665-12674 (1986) and Canalis et al., J. Clin. Invest. 81:277-281 (1988)). Eight BMPs have now been identified and are abbreviated BMP-1 through BMP-8. BMP-3 and BMP-7 are also known as osteogenin and osteogenic protein-1 (OP-1), respectively.
Unfortunately, DBM materials have little clinical use unless combined with particulate marrow autografts. There is a limit to the quantity of DBM that can be surgically placed into a recipient's bone to produce a therapeutic effect. In addition, resorption has been reported to be at least 49% (Toriumi et al., Arch. Otolaryngo. Head Neck Surg. 116:676-680 (1990)).
DBM powder and osteogenin may be washed away by tissue fluids before their osteoinductive potential is expressed. In addition, seepage of tissue fluids into DBM-packed bone cavities or soft-tissue collapse into the wound bed are two factors that may significantly affect the osteoinductive properties of DBM and osteogenin. Soft-tissue collapse into the wound bed may likewise inhibit the proper migration of osteocompetent stem cells into the wound bed.
Human DBM in powder form is currently used by American dentists to pack jaw bone cavities created during oral surgery. However, DBM in powder form is difficult to use.
Purified BMPs have osteoinductive effects in animals when delivered by a variety of means including FG (Hattori, T., Nippon. Seikeigeka. Gakkai. Zasshi. 64:824-834 (1990); Kawamura et al., Clin. Orthop. Rel. Res. 235:302-310 (1988); Schlag et al., Clin. Orthop. Rel. Res. 227:269-285 (1988) and Schwarz et al., Clin. Orthop. Rel. Res. 238:282-287 (1989)) and whole blood clots (Wang et al., J. Cell. Biochem. 15F:Q20 Abstract (1990)). However, Schwarz et al. (supra.) demonstrated neither a clear positive or negative effect of FG on ectopic osteoinduction or BMP-dependent osteoregeneration. Kawamura et al. (supra.) found a synergistic effect when partially purified BMP in FG was tested in an ectopic non-bony site. Therefore, these results are inconsistent and confusing.
TS also can serve as a "scaffold" which cells can use to move into a wounded area to generate new tissues. However, commercially available preparations of FG and other TSs are too dense to allow cell migration into and through them. This limits their effectiveness in some in vivo uses.
In one type of bone wound, called bone nonunion defects, there is a minimal gap above which no new bone formation occurs naturally. Clinically, the treatment for these situations is bone grafting. However, the source of bone autografts is usually limited and the use of allogeneic bones involves a high risk of viral contamination. Because of this situation, the use of demineralized, virally inactivated bone powder is an attractive solution.
D. Vascular Prostheses
Artificial vascular prostheses are frequently made out of polytetrafluoroethylene (PTFE) and are used to replace diseased blood vessels in humans and other animals. To maximize patency rates and minimize the thrombogenicity of vascular prostheses various techniques have been used including seeding of nonautologous endothelial cells onto the prothesis. Various substrates which adhere both to the vascular graft and endothelial cells have been investigated as an intermediate substrate to increase endothelial cell seeding. These substrates include preclotted blood (Herring et al., Surgery 84:498-504 (1978)), FG (Rosenman et al., J. Vasc. Surg. 2:778-784 (1985); Schrenk et al., Thorac. Cardiovasc. Surg. 35:6-10 (1986); Koveker et al., Thorac. Cardiovasc. Surgeon 34: 49-51 (1986) and Zilla et al., Surgery 105:515-522 (1989)), fibronectin (see, e.g., Kesler et al., J. Vasc. Surg. 3:58-64 (1986); Macarak et al., J. Cell Physiol. 116:76-86 (1983) and Ramalanjeona et al., J. Vasc. Surg. 3:264-272 (1986)), or collagen (Williams et al., J. Surg. Res. 38:618-629 (1985)). However, one general problem with these techniques is that nonautologous cells were used for the seeding (see, e.g., Schrenk et al., supra) thus raising the possibility of tissue rejection. In addition, a confluent endothelium is usually never established and requires months to do so if it is. As a result of this delay, there is a high occlusion rate of vascular prostheses (see, e.g., Zilla et al., supra).
E. Angiogenesis
Angiogenesis is the induction of new blood vessels. Certain growth factors such as HBGF-1 and HBGF-2 are angiogenic. However, their in vivo administration attached to: collagen sponges (Thompson et al., Science 241:1349-1352 (1988)); beads (Hayek et al., Biochem. Biophys. Res. Commun. 147:876-880 (1987)); solid PTFE fibers coated with collagen arranged in a sponge-like structure (Thompson et al., Proc. Natl. Acad. Sci. USA 86:7928-7932 (1989)); or by infusion (Puumala et al., Brain Res. 534:283-286 (1990)) resulted in the generation of random, disorganized blood vessels. These growth factors have not been used successfully to direct the growth of a new blood vessel(s) at a given site in vivo. In addition, fibrin gels (0.5-10 mg/ml) implanted subcutaneously in plexiglass chambers induce angiogenesis within 4 days of implantation, compared to empty chambers, or chambers filled with sterile culture medium (Dvorak et al., Lab. Invest. 57:673 (1987)).
F. Site-Directed, Localized Drug Delivery
An efficacious, site-directed, drug delivery system is greatly needed in several areas of medicine. For example, localized drug delivery is needed in the treatment of local infections, such as in periodontitis, where the systemic administration of antimicrobial agents is ineffective. The problem after systemic administration usually lies in the low concentration of the antimicrobial agent which can be achieved at the target site. To raise the local concentration a systemic dose increase may be effective but also may produce toxicity, microbial resistance and drug incompatibility. To circumvent some of these problems, several alternative methods have been devised but none are ideal. For example, collagen and/or fibrinogen dispersed in an aqueous medium as an amorphous flowable mass, and a proteinaceous matrix composition which is capable of stable placement, have also been shown to locally deliver drugs (Luck et al., U.S. Pat. No. Reissue 33,375; Luck et al., U.S. Pat. No. 4,978,332).
A variety of antibiotics (AB) have been reported to be released from FG, but only at relatively low concentrations and for relatively short periods of time ranging from a few hours to a few days (Kram et al., J. Surg. Res. 50:175-178 (1991)). Most of the ABs have been in freely water soluble forms and have been added into the TS while it was being prepared. However, the incorporation of tetracycline hydrochloride tetracycline hydrochloride (TET HCl) and other freely water soluble forms of ABs into FG has interfered with fibrin polymerization during the formation of the AB-supplemented FG (Schlag et al., Biomaterials 4:29-32 (1983)). This interference limited the amount and concentration of the TET HCl that could be achieved in the AB-FG mixture and appeared to be AB concentration dependent. The relatively short release time of the AB from the FG may reflect the relatively short life of the AB-supplemented TS or the form and/or quantity of the AB in the AB-TS.
G. Controlled Drug Release From TSs
For some clinical applications controlled, localized drug release is desirable. As discussed above, some drugs, especially ABs, have been incorporated into and been released from TSs such as FG. However, there is little or no control over the duration of the drug release which apparently is at least partially a reflection of the relatively short life of the drug-supplemented FG. Therefore, a means to stabilize FG and other TSs to allow for extended, localized drug release is desirable and needed, as are new techniques for the incorporation and extended release of other supplements from TS.
H. The Disclosed TS Preparations Provide Life-Saving Emergency Treatment for Trauma Wounds
Despite continued advances in trauma care, a significant percentage of the population, both military and civilian, suffer fatal or severe hemorrhage every year. An alarming number of fatalities are preventable since the occur in the presence of those who could achieve life-saving control of their wounds given adequate tools and training. The availability of the herein-disclosed TS satisfies the long-felt need for a advanced, easy-to-use, field-ready hemostatic preparation, to permit not only trained medical personnel, but even untrained individuals to rapidly reduce bleeding in trauma victims. Utilization of the disclosed TS preparations will result in a two-fold benefit: the reduction of trauma death, and the decreased demand upon the available blood supply.
The disclosed technology would also be available for the treatment of massed casualties in disaster situation. When severe natural or man-made disasters occur, local hospitals and clinics may be overwhelmed by the number of individuals requiring trauma care. Combined with the isolating effects of such disasters, the resulting demand for blood and blood products often exceeds the locally available supplies. In many cases, the demand upon the local medical personnel also exceeds the availed number of trained individuals. As a result, less seriously injured persons may be turned-away or given sub-optimal care. The availability of the easy-to-use, self-contained TS preparations disclosed below will permit local medical personnel and disaster relief workers to provide the injured with temporary treatment until definitive care becomes available. Moreover, the disclosed TS preparations will permit self-treatment in disaster victims, until medical assistance can be provided.
Often the only form of medical treatment that can be applied under such circumstances to prevent death due to blood loss is pressure dressings, tourniquets and pressure points. Unfortunately, however, each of these treatments requires continuous monitoring and attention. Since such attention is not always possible in emergency or disaster situations, there is a clear need in the art for a simple, fast-acting, first-aid treatment which can successfully control excessive blood loss.
The application of the disclosed TS preparations to the military is readily apparent, particularly in isolated battlefield situations. The single greatest cause of death on the battlefield is exsanguination, which until now has accounted for up to 50% of all combat casualties.